I dont know much from your post about your pond size but in zone 7 the pond must be at least 2 feet deep in its deep zone to winter fish safely.

I use a small pump with no fountian head on it, just a hose barb about 2 inches long screwed into the port. It sits on the bottom at about the 16 inch depth and discharges stright up so it disturbs the water to a hight of about 2 inches. This maintains the hole in the ice and has worked well for the past 8 years. It is often referred to as a bubbler pump but has no air like the type you are talking about. I always have a spare in hand just incase but have not needed it yet.

Mike

I am no expert but I have tried various things and have made some observations.

A fountain is not useful to keep a hole in the ice. The fountain divides the water into small units that have more total exposed surface area as compared to the exposed surface of the pond. Each loses heat to the ambient atmosphere at the same rate but since there is more exposed surface area, the drops from the fountain lose more heat overall.

A bubbler ordinarily used for an aquarium moves the water so that at least the column of water affected is continuously being refreshed from the bottom. While the water is exposed on the surface to lower temperatures and loses some heat, it loses less to the air because of the exposure time element. The major loss is to the surrounding ice which reduces the ice and enlarges or maintains the hole. The drawbacks to the aquarium bubbler are the materials used in construction, the efficiency of the protection of the device including the tubing from the elements, positioning of the bubbler end and the quantity and size of the bubbles.

A good quality bubbler for a twenty gallon plus aquarium is sufficient for my 1000 gallon pond with a three foot depth in zone 5. It produces a hole at least one foot wide in severe temps. The ice in a two to three foot diameter is visibly thinner beyond the actual hole. Beyond that the ice gets much thicker.When I run the Skippy filter the hole and thin ice get larger since the moving water mixes warmer water into the system. Over all the temperature of the water may get cooler but so long as it is above the freezing point the hole(which is the whole point)remains open.

I put the bubbler motor inside a small weather and mostly waterproof container along with the receptacle for the plugs for the pump and lights if I am using them. The heat generated by those keeps the air forced through the tubes relatively warm. I use silicone tubing since it is less affected by the temperatures. The rubber in the diaphragms in the air pump are not as badly degraded as they are by exposure to more severe low temps outside the container. The container is kept as close to the edge of the pond as possible to reduce heat loss and in really severe weather I may cover the tubing with something or run it through a foam sleeve. All I really need is to prevent any moisture from freezing inside the tubing.

There has been some discussion over the distance from the bottom the diffuser end should be placed. Since the bottom of my pond is sloped and I try to keep debris at a minimum , all I do is position it above the area where any debris would settle. I notice the area around the diffuser stays clear though when it is on the bottom. DRH1 and Michael had a discussion on this subject that you might find interesting if you do a search. Remember, my observations are just observations.

A diffuser that puts out a lot of small bubbles seems to be much more efficient than one that puts out large bubbles. The fish like the small bubbles.

The major advantages of the outdoor model are that it is underwater which protects it from ambient weather and you don't see it.

The weakest point of the aquarium bubbler is the diaphragm. Eventually they do wear out from the constant flexing. I used to be able to buy replacements but they no longer seem to be available.

I am going to try out a bubbler for a 400 gallon Aquarium this season.

I stopped using deicers. They didn't add enough to the effects of the bubbler to justify their use or their expense.

I'm switching back to a bubbler this year. I bought a good pump on Amazon - Hydrofarm AAPA15L 6-Watt 15-LPM Active Aqua Air Pump for ~$20. Ordered yesterday - shipped today.

I also found a few other of the items needed on Amazon. (Free shipping on orders over $25. and, for me, no tax.) Much more economical than buying locally.

(Hope I can post this type of information on GW.)

Gail

I use a bubbler till it gets too cold (se Michigan ) then have to use my deicers. Last winter was mild so I don't think I used the deicer. I have about 25' of tubing coming thru my garage window with air pump inside garage where it doesn't get below 40 degree in winter. Only pita is the tubing ices up and I have to hold it to thaw ice to get air moving through again.